Gosh that's really tricky.
NVR stands for non violent resistance, and it is linked with therapeutic parenting. It's a way of parenting that reduces demands on a child whose negative behaviours indicate they are overwhelmed, which it sounds like may be the case here.
A key thing to consider would be liaising with the young person's school and any other services that they are engaged with in order to get a fuller picture of where they are at and what can be done to support them. Most teens are dicks for a significant portion of their teenage years, try not to hold it against them too much!
The fact that you don't already have children may actually be helpful because you have fewer preconceived ideas about where the child "should" be at and no competing dependents (barring any other caring responsibilities) so you can be focused on exactly on what the child needs and parenting them how they need rather than how you had done something in the past or thought it should be done. However, I you were child free by choice, it's a big ask, and I should imagine you are feeling from the significant life changes.
Do you have any idea what the plan is moving forward? I would say that there is possibly some merit in familiarising yourself with adoption introduction strategies that, although aimed at younger children, provide a framework of transition for moving from one setting to the next. Silly things like having the same washing powder, knowing how much pocket money they get, knowing how to work the shower, you getting access to be able to monitor their social media, school records changed over, medical records changed, stuff like that will all need to be considered.
I also just wanted to acknowledge that I presume you have lost someone close or connected to you too. It's important to look after yourself and have this built into whatever care you will provide. Wherever possible lean on your support between to help you, to monitor and guide you both. Take time for yourself and allow yourself to feel what you need to feel. It's ok to be angry, sad, mad, frustrated and relieved all at once, and caring for someone else who is traumatised and grieving can make your own burden even more difficult, especially if you are thrown in at the deep end.
Is there any specific information that you think would be helpful? Sometimes in unexpected and quickly changing situations it can be helpful for the internet hivemind to do some thinking, even if it just a list of questions to ask school when you meet with them or a list of stuff that teenage boys use on a daily basis. I'm sure people would be happy to help!